It has long been appreciated that differential air pressure may be utilized to retain a prosthetic limb on a patient's limb or stump. Gravitational and other forces tend to cause separation between the prosthetic limb and the patient's residual extremity during use. This happens, for example, during the swing phase of gait, when a prosthetic leg is additionally subjected to centrifugal forces. Patients have routinely worn a variety of belts, straps, cuffs and harnesses to retain their prosthetic limbs against separation from the residual limb. In addition, a variety of socket configurations have been utilized for the same purpose. However, none of these can provide the reliable, strong retentive force which is provided by differential air pressure in accordance with the present invention.
For many years differential air pressure or "suction" sockets have been utilized with reasonable success in prosthetic limbs for selected above-knee amputees. However, there has been a corresponding lack of success in using such sockets for other levels of amputation. The basic reason for this is that the relatively soft, fleshy characteristics of a residual above-knee stump, in conjunction with tightly fitting proximal socket walls serves as a seal to preserve a partial vacuum within the socket. In the case of other amputees whose belowknee, upper-limb and other above-knee residual limbs lack the prerequisite characteristics, it has been impossible to use suction successfully with any frequency, because of the tendency for gaps and channels to form between the stump and the socket walls with a resultant loss of suction or partial vacuum within the socket.
Most amputees wear woven "stump socks" as an interface between their skin and the prosthetic socket for increased comfort, perspiration absorption, and reduced friction. These socks vary from thin sheaths (about 0.010-0.015 inches thick) to rather thick socks (about 0.125 inches thick) which are used to accommodate substantial discrepancies between stump shapes and volumes in relation to the prosthetic socket. All of these socks, regardless of the material from which they are fabricated (nylon, orlon, cotton, wool, etc.) are porous. As such, air flows freely past the proximal borders of the socket, making it impossible to maintain a vacuum within. The same problem of uncontrolled air leakage can exist when no stump sock is worn.
Broadly, it is an object of the present invention to overcome the shortcomings of known artificial limbs utilizing differential air pressure, which shortcomings result in the inability to reliably and consistently retain the prosthesis on the patient's residual limb. It is a specific object of the present invention to create an air seal between the socket of the prosthesis and the residual limb, so that air leakage and the accompanying loss of vacuum may be avoided. As a result, a great many well-fitted prosthetic sockets may be used in the same manner as a suction socket, when the patient wears a prosthetic sock in accordance with the present invention.
It is another object of the present invention to provide a prosthetic sock, which may be worn by a patient over his stump, in order to provide consistent and reliable air sealing between the socket of the prosthesis and the patient's stump, thereby making it possible to retain a great many wellfitted artificial limbs by means of differential air pressure.
It is another object of the present invention to provide an improved construction for the stump-receiving socket of an artificial limb which will provide a consistent and reliable air seal between the socket and the patient's stump, regardless of the characteristics or morphology of the stump.
It is yet another object of the present invention to provide a method for fabricating a prosthetic sock and a stumpreceiving socket for an artificial limb in accordance with the two immediately preceding objects.
It is also an object of the present invention to provide a stump-receiving socket for an artificial limb, a prosthetic sock useful in retaining well-fitted artificial limbs, and a method for manufacturing the same, which are reliable and convenient in use, yet relatively inexpensive.
In accordance with the present invention, an air impermeable, elastic sealing band is introduced between the interior of the stump-receiving socket and the patient's stump in one of two ways, depending on whether or not the patient wears a stump sock. If the patient wears a stump sock, the sealing band is impregnated into the stump sock. If the patient does not wear a stump sock, the impregnated sock is incorporated into the structure of the socket of the patient's prosthesis.
The impregnated prosthetic sock itself is preferably fabricated by placing a conventional stump sock on a somewhat oversized cylindrical or conical form shaped generally like the stump. An appropriate annular region on the sock is then masked off by means of tightly fitting plastic bags, and one of the plastic bags provides a enclosing outer sheath which encompasses the annular region and extends upwardly above the form. A rubberized material in liquid form is introduced through the top of this outer sheath bag, and a vacuum is introduced below to draw the material into the annular region of the sock so as to impregnate the same. The rubberized material penetrates the sock, is worked into an axially contoured shaped, and is then permitted to set. After the sealant material is fully cured, the plastic bags may be discarded and the sock removed from the form.
A stump-receiving socket with an integral annular seal is preferably fabricated by placing a prosthetic sock with an impregnated seal on the cast of a patient's residual limb and then forming the stump-receiving socket, by lamination, over the sock using conventional procedures for manufacturing sockets.